Group III-V compound semiconductors such as GaN and AlGaN are widely used in optoelectronics and for electronic devices by virtue of many advantages thereof, for example, wide and easy-adjustable band gap energy.
In particular, light emitting devices, such as light emitting diodes (LEDs) and laser diodes, which use a Group III-V or Group II-VI compound semiconductor material, may render various colors such as red, green, blue, and ultraviolet by virtue of development of thin film growth technologies and device materials. It may also be possible to produce white light at high efficiency using fluorescent materials or through color mixing. Further, light emitting devices have advantages, such as low power consumption, semi-permanent lifespan, fast response time, safety, and environmental friendliness as compared to conventional light sources, such as fluorescent lamps and incandescent lamps.
Therefore, these light emitting devices are increasingly applied to transmission modules of optical communication units, light emitting diode backlights as a replacement for cold cathode fluorescent lamps (CCFLs) constituting backlights of liquid crystal display (LCD) devices, and lighting apparatuses using white light emitting diodes as a replacement for fluorescent lamps or incandescent lamps, headlights for vehicles and traffic lights.
In a conventional light emitting device, a light emitting structure including an undoped semiconductor layer (un-GaN), a first conductivity type semiconductor layer (n-GaN) an active layer (multi-quantum well (MQW)) and a second conductivity type semiconductor layer (p-GaN) is formed on a substrate made of sapphire or the like. First and second electrodes may be disposed on the first conductivity type semiconductor layer and second conductivity type semiconductor layer, respectively.
The light emitting device emits light having energy determined by an intrinsic energy band of the material of the active layer when electrons injected into the active layer via the first conductivity type semiconductor layer recombine with holes injected into the active layer via the second conductivity type semiconductor layer. Light emitted from the active layer may vary in accordance with the composition of the material of the active layer. The light may be blue light, ultraviolet (UV) light, deep UV light or light of other wavelength ranges.
FIG. 1 is a view illustrating a conventional light emitting device.
The light emitting device, which is designated by reference numeral “100”, includes a substrate 110, a light emitting structure formed on the substrate 110 while including a first conductivity type semiconductor layer 122, an active layer 124 and a second conductivity type semiconductor layer 126, a transmissive conductive layer 150 formed on the light emitting structure 120, a first electrode 180, and a second electrode 185.
When the second conductivity type semiconductor layer 126 is a p-GaN layer, inferior current spreading effects may be exhibited. For this reason, the transmissive conductive layer 150 is disposed on the second conductivity type semiconductor layer 126 so as to receive current from the second electrode 185.
In this case, however, light emitted from the light emitting structure 120 may be partially absorbed by the transmissive conductive layer 150. Furthermore, there may be a problem in that the light emitting device 100 has a narrow orientation angle.